1. Field of the Invention
The present invention relates to a method and apparatus for dewatering sludge wastes discharged from various factories, such as a paper pulp factory, a chemical factory and a food factory.
2. Related Art Statements
Heretofore, sludge wastes of the paper industry has been treated in the following manner. The sludge wastes are first supplied to a clarifier to settle solid substances, and then the settled sludge is introduced into an agglutinating reaction tank to which a macromolecular agglutinating agent is also supplied by such an amount that it is substantially proportional to an amount of the introduced sludge. Next, the thus agglutinated sludge is supplied to a dewatering device such as a screw press and dewatered solid substances are discharged or burned at a predetermined waste treating site.
FIG. 1 is a schematic view showing a known sludge treating system for performing the known sludge treating method. A settled sludge S discharged from the above mentioned clarifier is supplied into an agglutinating reaction tank 2 having an agitator 1 installed therein. Into the agglutinating reaction tank 2 an agglutinating agent P consisting of various kinds of macromolecular substances is supplied to carry out the agglutinating reaction. Then, the agglutinated sludge is supplied via a preliminary dewatering device 3 to a main dewatering device 4 formed by a screw press. Solid substances, i.e. a dewatered cake Sa, is burned or discharged at a waste treating site and a waste water L discharged out of the screw press 4 is supplied to the clarifier 2. A supernatant in the clarifier 2 is discharged out of the sludge treating system.
In the known pulp sludge treating system, the macromolecular agglutinating agent is supplied into the clarifier 2 by such an amount that it is proportional to a total amount of the pulp sludge supplied from the factory into the agglutinating reaction tank, otherwise the dewatering efficiency might be decreased. Therefore, a large amount of the expensive agglutinating agent, such as 230 kg/day, has to be introduced into the agglutinating reaction tank 2, and the operating cost for treating the sludge tends to be high. Particularly, in the paper pulp factory a very large amount of the sludge is produced and thus a very large amount of the macromolecular agglutinating agent is used. This causes a serious problem.